Learning to swim and training to become a better swimmer are both facilitated by the trainee or swimmer practicing exercises and repetitive routines. The exercises help to refine the motions that the swimmer should use to swim efficiently. Some exercises also strengthen the muscles that are used in making the swimming motions.
It is well known that weight training, or weight lifting can improve a swimmer's performance due to the increased strength resulting from the weight training. There are many forms of weight training. The trainee can use free weights of various weights, shapes and sizes, and can move them about according to many different patterns. The trainee can also use weight training machines, which generally provide a specific staging devoted to development of a particular muscle or muscle group. The staging forces the user to apply muscular force against a resistance and to move his/her limbs through a specific path. The resistance can be provided by stacks of weights engaged by pulleys. The resistance can also be provided by pneumatic cylinders, or by cams connected to large inertial masses. Typically, the user can quickly adjust the amount of weight, or pneumatic resistance, so that the user can change the weight he/she is using, or so that the machine can be used by many different users of different strengths, or following different exercise regimens.
It is also well known that an athlete's muscles develop in a way that is desirable for practice of a particular sport or motion by the actual practice of that sport or motion. Thus, the muscles that a sprinter needs develop by virtue of sprinting. The muscles that a swimmer needs develop by virtue of swimming. It has also been known that the athlete's muscles grow larger, or develop more quickly, if they are applied to overcome a resistance that is greater than that typically encountered by the actual sport, if the resistance is applied in a way that simulates the motions that the athlete should use when actually performing the sport. Thus, the prevalence of stationary bicycles, rowing machines and cross-country ski simulators.
Known devices, referred to as "swim benches," attempt to simulate the swimming action with a resistance for weight training. In the most rudimentary design, the swim bench includes a bench or platform on which the swimmer lies, and handles or paddles attached by cable to weights that move up and down as the swimmer completes and returns each stroke. Although such a device exercises the muscles used in swimming, the dynamic forces required to lift a weight against gravity do not simulate the dynamic forces exerted on the hands and body while swimming. Thus, the rudimentary swim bench does not accurately simulate swimming. It does not feel like swimming to the user. An additional drawback of using this sort of a weight resistance is that there is not damping to slow the weight down at the end of the stroke. Thus, the user must slow hand motion down at the end of the stroke to keep the weight from flying out of control. In swimming, as explained below, it is desirable to accelerate at the end of the stroke, rather than slowing down.
In order to explain the operation of known devices, and point out their drawbacks, it is necessary to present the inventor's theory of the dynamics of swimming. This theory is the inventor's own, and its development is considered to be part of the invention.
Very little research has been conducted regarding the dynamics of the swimming stroke. However, several factors have been identified by experienced swimmers. For instance, a higher resistance to hand motion arises in response to higher hand velocities. Further, at high swimming speeds, the forward speed immediately decreases if the stroke slows. It is also important to note that, to swim quickly, an experienced swimmer accelerates the hand at the end of the stroke. Thus, this sort of hand motion should be permitted. That is, for instance, there should not be any artificial impediment which increases the resistance to the hand at the end of the stroke simply by virtue of the position of the hand. Another impediment to this acceleration at the end of the stroke is a weight that has been previously accelerated by the user, and that must be slowed down at the end of the stroke.
The inventor believes that the foregoing swimmers' experiences can be provisionally formalized as follows. The torso and legs can be modeled like the hull of a ship. The dynamics of the hand and body motion are shown schematically in FIGS. 6a, 6b and 7. FIG. 6a shows schematically a swimmer 600 swimming through the water in three positions: beginning (600b in bold line), middle (600m, in normal line) and end of a stroke (600e, in dotted line) with the right arm, similarly designated 602b, 602m and 602e. (For clarity, the swimmer's left arm is not shown.)
In an ideal situation, a swimmer would cast an arm 602 forward, plant it in the water, and then pull the body 600 through the water, past the hand, and beyond, just as if a bar were fixed in the water and the swimmer were pulling himself through the water by grasping the bar. However, this situation does not exist in water, since there is no bar and water can not be grasped firmly. Some of the water moves backward in response to force applied to it, and further, some of the water leaks around the swimmer's hand and through the swimmer's fingers.
If there were a bar, the swimmer's hand would be stationary with respect to the bar (and the pool foundation) during the catch portion of a stroke, as the body moved forward. The hand would not move forward until the return portion of the stroke brings it out of the water and around. In reality, however, the hand moves backward a small amount during the course of the stroke. This is indicated by the three hand positions 604b (beginning of stroke), 604m (middle of stroke) and 604e (end of stroke). Thus, relative to the pool foundation, during the course of a single stroke, the swimmer's torso moves forward a distance t, while the hand moves backward a distance h. The better the swimmer, the smaller the distance h. Further, the quicker the stroke, the smaller the distance h. For a competent swimmer, swimming moderately fast, h is on the order of six inches (15 cm) and t is on the order of four to five feet (1.5 m), depending on the swimmer's height.
FIG. 7 shows the local environment around the swimmer's body 700 during a stroke. The body is being pulled and forced through the water by the swimmer's hand and arm. The water flows around the swimmer's body. (Relative to the body, if considered stationary, the water flows in the direction indicated by streamlines W. Relative to the stationary pool foundation, the water is virtually stationary and the body moves in the direction of the dotted arrow B.) Like any object in a fluid flow, the water presents a viscous force against the relative motion of the body. Since the water is virtually stationary with respect to the pool foundation, the relative velocity is essentially equal to the velocity of the swimmer's body to the pool foundation.
An additional force also opposes the motion of the body. This force is known as a "pressure drag" which arises due to the fact that turbulence is generated downstream of the body (i.e., at location 708), thereby causing a pressure differential between the upstream end 706 of the body 700 and the downstream end 708, tending to push the body 704 in the direction from high pressure to low pressure, i.e. in the direction the fluid is flowing relative to the body. This is opposite to the direction that the swimmer's body is moving, relative to a stationary pool foundation.
The inventor believes that both the viscous and the pressure drag forces are proportional to the cube of the relative velocity between the fluid and the body.
For a body moving through a fluid, the foregoing fluid dynamics result in a component of the force on the swimmer's body according to the following formula: EQU F=K*V.sub.body.sup.3
where K is a constant related to each swimmer's body shape.
The swimmer's hand also experiences the same sorts of viscous and pressure drags, however they are applied to the hand in the opposite direction from which they are applied to the body, since the relative motion between the hand and the water is opposite to that of the body and the water.
The force set forth above is the force that the swimmer must apply to his body to move the body at the speed V.sub.body. Ignoring the swimmer's kick, all of this force must be applied by virtue of interaction between the swimmer's arms, hands and the water. Thus, the force applied by the water to the swimmer's hands and arms is also proportional to the cube of the velocity of the swimmer's body.
The inventor believes that, while the foregoing theoretical explanation is apt, other factors may contribute to the forces experienced by the hands and arms moving through the water such that the force applied by the water is proportional to the velocity of the body raised to a factor greater than two and less than or equal to three. This belief is supported by subjective experiments, comparing the feel of different types of swim benches to actual swimming.
With some types of swim benches, including the type of the present invention, the swimmer's body is stationary relative to the ground, and the swimmer's arms move against a resistance. This is analogous to the situation during actual swimming, as viewed from the position of the swimmer's body. It seems that the body remains stationary as a stream of water flows from the swimmer's head to his feet, with the swimmer's hands moving past the swimmer's body at approximately the speed of the water. This situation is shown schematically in FIG. 6b. The swimmer's body, 600, remains stationary, while three arm positions, beginning (604b), middle (604m) and end (604e) are shown respectively. The total distance the swimmer's hand moves relative to the body is equal to the distance t the torso would move forward in the water relative to the pool foundation, minus the distance that the swimmer's hand moves relative to the swimmer (h), for a total distance of t-h. Thus, during the same time, the swimmer's body moves a distance t through the water, while the stationary trainee's hand moves a distance t-h in the opposite direction through the air. As has been mentioned, for better, more efficient swimmers, the slippage distance, h, is approximately equal to zero.
Thus, for a trainee using a swimming bench, the speed of the hand is approximately equal to the speed the swimmer's body would be moving through water. As mentioned above, the inventor believes that the force experienced by a swimmer's hand while moving the body through the water includes a component that is proportional to the cube of the velocity of the body (or proportional to a power of the velocity of the body greater than two and less than or equal to three). Since the velocity of the hand through the air is approximately equal to the velocity of the body through the water, it follows that if a force is applied to the hand that includes a component that is approximately proportional to the cube of its velocity through the air (or a power of the velocity greater than two and less than or equal to three) for the velocities in question, that force will simulate the force that the hand actually feels when moving the body through the water. It will feel to the trainee as if he is moving his hand against water in the act of swimming.
Other swim benches have been proposed and used, differing from the rudimentary design mentioned above (lifting a weight against gravity), principally in the resistance mechanism. One resistance mechanism is a spinning inertial mass connected to the cables. As the hand paddles are accelerated, the forces on the hand increase proportionally to the angular acceleration of the mass. The force to increase a velocity of the hand pulling the paddles, is equal to the inertial mass, times the angular acceleration of the mass (which is directly proportional to the translational acceleration of the paddles). Once the disk is spinning fast enough, the swimmer can stroke quickly from the start and accelerate through the finish of the stroke, as is desired for a fast swim.
A drawback of the inertial mass as the resistive element, is that there is no way to adjust the resistance, so it is difficult to accommodate multiple users having strengths spread over a wide range. Further, it is possible to cause the disk to spin so fast, that the arms must move faster than is reasonably possible in the water to keep up with the disk. Consequently, it becomes more difficult to accelerate the arm through each stroke, thus detracting from the accuracy with which the apparatus simulates swimming. Most importantly, the spinning inertia does not present a resistance that feels at all like swimming.
Another proposed resistance mechanism is commonly used, and is similar to stretching a large rubber band or rubber tubing. This mechanism has the advantage that it is simple to implement. The tubing is attached to the handles upon which the swimmer pulls. The resistance force applied to the hand is equal to the spring constant of the tubing times the distance the tubing is stretched from its rest position. Consequently, to move the same distance, the greatest force is applied to the hand at the finish of the stroke. The initial tension can be adjusted, for instance by pre-stretching the rubber element.
A major drawback with this spring resistance apparatus is that it provides no simulation of the relation between force and the cube of hand velocity believed to exist in swimming. Thus, it does not feel like swimming. Typically, the spring constant of a rubber band-like tubing decreases at higher velocities, thus lowering the force required to cause a further extension. However, in swimming, the force at higher velocities increases.
Another form of known apparatus is an inclined monorail with a sliding bench. Such an apparatus is sold by Vasa Inc., of Williston, Vt. under the trade name "Vasa Swim Trainer." The swimmer lies on a bench and pulls on a pair of handles at the ends of a pair of inextendible cables or tethers. The handles do not move longitudinally with respect to the monorail, but they can move transverse of the monorail axis, essentially swinging in an arc with a radius that is the length of the tether. As the user applies force to the handles, the bench slides longitudinally along the monorail toward the handles. The user's body passes his/her hands, which move outward. Resistance is applied due to the incline of the bench, which is variable, and tension (apparently a spring). After each stroke, the swimmer relaxes and the tension and gravity pulls the bench back to the beginning of the monorail. The monorail is typically about eight feet long.
This system suffers from some of the drawbacks mentioned above in that it does not simulate the dynamic forces of swimming believed to be related to the cube of hand velocity. Consequently, it does not feel like swimming. Further, for strokes where each hand moves forward individually, such as the free-style, the body must move backward on the monorail before the opposite hand can be pulled. This jerky motion is far from that which is felt during swimming. Further, it is difficult to accelerate the hand at the end of the stroke, because at that phase of the stroke, the force applied by the tension in the spring is near its greatest, since it is near its fullest extension. The restrained hand motion also minimizes the verisimilitude the apparatus can offer. It is important to have the hand pass near to the body, not far from it. In most strokes, the swimmer must bring his hand either under, or to some extent, across his body. The Vasa trainer monorail prohibits passing the hand underneath the swimmer's body, particularly ahead of the body. Thus, this type of swim trainer does not exercise the muscles actually used in swimming.
U.S. Pat. No. 5,029,848 issued to Sleamaker on Jul. 9, 1991, discloses a monorail device that is similar to the Vasa trainer.
Another known apparatus is described in U.S. Pat. No. 4,830,363, issued to Kennedy on May 16, 1989, which discloses an apparatus having a frame supporting a bench on which the user's torso is supported generally horizontally. Handles are provided attached to retractable cords and mounted on the frame. A tensioning means is provided to retract the cords, but its dynamic specifications are not noted. The bench has a vertically adjustable middle section, so that a bend of the user's body at the waist can be accommodated.
U.S. Pat. No. 3,791,646, issued to Marchignoni on Feb. 12, 1974, discloses an apparatus having a box support on which the user lies, and two triangularly shaped arm units. The box and triangular units house a geared mechanism that provides a resistance. The arms pull on levers that are attached to an anchor that is constrained to travel according to an elliptical path. The device includes an electric motor, which drives the anchors around the elliptical paths, as well as stirrups for the legs.
An additional drawback of all of the known devices is that none accommodate the rocking or rolling motion that is attendant to swimming motions using alternate hand motion, such as the free-style and backstroke. Typically, in such a stroke, as the swimmer finishes each stroke, the body rolls downward toward the side where the arm is pulling through the water. During the execution of these strokes it is critical that the hips remain stationary while the torso is rolled towards that side of the body where the arm is pulling through the water. It is well known that the hips should remain as close as possible to the horizontal position to maintain proper body orientation for the most efficient swimming strokes. In order to effectively simulate this smooth rolling motion with a machine the chest should be cradled in a device which allows an independent rolling motion of the torso while keeping the hips fixed in a horizontal position.
U.S. Pat. No. 4,674,740 issued to Iams et al. on Jun. 23, 1987, discloses a swimming trainer which allows for a rocking motion of the body during execution of the stroke. The drawback of this machine is that the entire body rocks because the entire frame moves as one. It is commonly recognized in the swimming world that the upper and lower body must move independently of each other to properly simulate swimming.
U.S. Pat. No. 5,158,513 issued to Reeves on Oct. 27, 1992, reveals a swimming training apparatus in which the user's body is supported in a generally horizontal position so the user can pull against hand paddles which activate a resistance mechanism. The unique thing about the apparatus is that it allows for independent rotation of a head support, the chest support, and the hip support. It appears that this meets the objectives of the inventor's design. The inventor believes that Reeves' apparatus would be very awkward to use because it does not cradle the user's chest. Furthermore the apparatus which allows for chest rotation forces the chest out of line with the head because its center of rotation is below the body. Using proper stroke technique the body should rotate about a center axis which is approximately in line with the spine of the body. Thus Reeves' apparatus does not simulate the rocking motion of swimming in the way the inventor believes is critical to proper body orientation.